Tesi sul tema "Coronagraphie"

L’imagerie directe des exoplanètes reste difficile en raison du contraste élevé et de la faible séparation angulaire entre l'étoile et la planète. Cela nécessite de supprimer l'éblouissement dû à l'étoile et de s'assurer que la lumière faible de la planète n'est pas noyée au milieu de divers bruits. La détection dépend de la maturité des techniques et des algorithmes utilisés, tout en tenant compte des compromis importants sur le contraste brut, la résolution angulaire et la transmission. L'une de ses composantes clés est l'utilisation de coronagraphes - des instruments ayant pour seul but de bloquer/réduire la lumière provenant de l'étoile. Ce travail présente un nouveau type de coronographe de Lyot, inventé par le Dr Yves Rabbia, qui repose sur le principe de la réflexion interne totale frustrée (FTIR) pour supprimer la lumière de l'étoile. Ce coronographe est appelé Evanescent Wave Coronagraph (EvWaCo) en raison de sa nature : son masque au plan focal, comprenant une lentille et un prisme, réfléchit la source hors axe (planète) et transmet la source sur l'axe (étoile) à l’aide des ondes évanescentes. Cette thèse vise à fournir au lecteur les bases qui mettent en évidence les trois principaux avantages d'EvWaCo : i) le masque est intrinsèquement achromatique, ii) la taille du masque est ajustable en modifiant la pression entre la lentille et le prisme, et iii) à la fois la lumière stellaire et la lumière planétaire peuvent être collectées simultanément pour une détection de front d'onde de bas ordre et un centrage approprié de l’étoile. Les performances d'EvWaCo sont évaluées à travers des expériences en laboratoire, puis comparées à des simulations numériques. Les résultats expérimentaux montrent un contraste brut égal à quelques 10-4 à 3 ��/�� sur toute la bande I (��c = 800 nm, ∆��/�� ≈ 20%) et à 4 ��/�� sur toute la bande R (��c = 650 nm, ∆��/�� ≈ 23%). Les simulations confirment la capacité de rejet achromatique d'EvWaCo, montrant un contraste brut de 10-4 à la même distance radiale sur les deux bandes spectrales. Cette thèse se conclut sur un bilan de l’état du banc développé et les perspectives futures
Direct imaging of exoplanets remains challenging due to the high contrast and the small angular separation between the star and the planet. It requires suppressing the blinding glare from the star and ensuring that the planet's faint light is not buried deep in various noises. Successful detection depends on the technological readiness and maturity of techniques and algorithms employed while considering the significant trade-offs on raw contrast, inner working angle, and throughput. One of its key components is the use of coronagraphs – instruments with the sole purpose of blocking/reducing the light from the star. This work presents a new type of Lyot coronagraph, invented by Dr. Yves Rabbia, that relies on the frustrated total internal reflection (FTIR) principle to suppress the starlight. This coronagraph is aptly called the Evanescent Wave Coronagraph (EvWaCo) owing to its nature that its focal plane mask, comprising a lens and a prism, reflects the off-axis source (planet) and transmits the on-axis source (star) by capturing the evanescent waves. This thesis aims to provide the reader with the groundwork that highlights EvWaCo's three main advantages: i) the mask is inherently achromatic, ii) the size of the mask is adjustable by changing the pressure between the lens and the prism, and iii) both the stellar light and the planet light can be collected simultaneously for low-order wavefront sensing, and proper stellar light centering. The performance of EvWaCo is assessed through experiments in a laboratory and then compared to numerical simulations. The experimental results show a raw contrast equal to a few 10-4 at 3 ��/�� over the full I-band (��c = 800 nm, ∆��/�� ≈ 20%) and at 4 ��/�� over the full R-band (��c = 650 nm, ∆��/�� ≈ 23%). The simulations confirm the achromatic rejection capability of EvWaCo as it showed a raw contrast of 10-4 at the same radial distance over both bandpasses. This thesis concludes with the status of its testbed and future perspectives

The point spread function (PSF) for astronomical telescopes and instruments depends not only on geometric aberrations and scalar wave diffraction, but also on the apodization and wavefront errors introduced by coatings on reflecting and transmitting surfaces within the optical system. Geometrical ray tracing provides incomplete image simulations for exoplanet coronagraphs with the goal of resolving planets with a brightness less than 10<^>-9 of their star located within 3 Airy disk radii. The Polaris-M polarization analysis program calculates uncorrected coating polarization aberrations couple around 10<^>-5 light into crossed polarized diffraction patterns about twice Airy disk size. These wavefronts not corrected by the deformable optics systems. Polarization aberrations expansions have shown how image defects scale with mirror coatings, fold mirror angles, and numerical aperture.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, May, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 71-76).
High contrast astronomy has yielded the direct observations of over a dozen exoplanets and a multitude of brown dwarfs and circumstellar disks. Despite advances in coronagraphy and wavefront control, high contrast observations are still plagued by residual wavefront aberrations. Post-processing techniques can provide an additional boost in separating residual aberrations from an astrophysical signal. This work explores using a coronagraph instrument model to guide post-processing. We consider the propagation of signals and wavefront error through a coronagraphic instrument, and approach the post-processing problem using "robust observables." We model and approximate the instrument response function of a classical Lyot coronagraph (CLC) and find from it a projection that removes the dominant error modes.
We use this projection to post-process synthetically generated data, and assess the performance of the new model-based post-processing approach compared to using the raw intensity data by calculating their respective flux ratio detection limits. We extend our analysis to include the presence of a dark hole using a simulation of the CLC on the High-contrast imager for complex aperture telescopes (HiCAT) testbed. We find that for non-time-correlated wavefront errors, using the robust observables modestly increases our sensitivity to the signal of a binary companion for most of the range of separations over which our treatment is valid, for example, by up to 50% at 7.5[lambda]/D. For time-correlated wavefront errors, the results vary depending on the test statistic used and degree of correlation. The modest improvement using robust observables with non-time-correlated errors is shown to extend to a CLC with a dark hole created by the stroke minimization algorithm.
Future work exploring the inclusion of statistical whitening processes will allow for a more complete characterization of the robust observables with time-correlated noise. We discuss the dimensionality of coronagraph self-calibration problem and motivate future directions in the joint study of coronagraphy and post-processing.
by Yeyuan (Yinzi) Xin.
S.M.
S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics

In preparation for the Astro 2020 Decadal Survey NASA has commissioned the study four flagship missions spanning to a wide range of observable wavelengths: the Origins Space Telescope (OST, formerly the Far-Infrared Surveyor), Lynx (formerly the X-ray Surveyor), the Large UV/Optical/Infrared Surveyor (LUVOIR) and the Habitable Exoplanet Imager (HabEx). One of the key scientific objectives of the latter two is the detection and characterization of the earth-like planets around nearby stars using the direct imaging technique (along with a broad range of investigations regarding the architecture of and atmospheric composition exoplanetary systems using this technique). As a consequence dedicated exoplanet instruments are being studied for these mission concepts. This paper discusses the design of the coronagraph instrument for the architecture "A" (15 meters aperture) of LUVOIR. The material presented in this paper is aimed at providing an overview of the LUVOIR coronagraph instrument. It is the result of four months of discussions with various community stakeholders (scientists and technologists) regarding the instrument's basic parameters followed by meticulous design work by the the GSFC Instrument Design Laboratory team. In the first section we review the main science drivers, presents the overall parameters of the instrument (general architecture and backend instrument) and delve into the details of the currently envisioned coronagraph masks along with a description of the wavefront control architecture. Throughout the manuscript we describe the trades we made during the design process. Because the vocation of this study is to provide a baseline design for the most ambitious earth-like finding instrument that could be possibly launched into the 2030's, we have designed an complex system privileged that meets the ambitious science goals out team was chartered by the LUVOIR STDT exoplanet Working Group. However in an effort to minimize technological risk we tried to maximize the number of technologies that will be matured by the WFIRST coronagraph instruments.

Described here is the design, manufacturing, testing and commissioning of a coronagraph facility for the 4.2 metre William Herschel Telescope (WHT) and its adaptive optics system (NAOMI). The use of the NAOMI adaptive optics system gives an improved image resolution of ~ 0.15 arcseconds at a wavelength of 2.2μm. This enables the Optimised Stellar Coronagraph for Adaptive optics (OSCA) to null stellar light with smaller occulting masks and thus allows regions closer to bright astronomical objects to be imaged. OSCA is a fully deployable instrument which when in use leaves the focus of the NAOMI beam unchanged. This enables OSCA to be used in conjunction with a number of instruments that have already been commissioned at the WHT. The main imaging camera used with OSCA is INGRID; a 1024 × 1024 pixel HgCdTe cooled short-wave infra-red (SWIR)detector at the NAOMI focus. OSCA also has the option of being used in conjunction with an integral field spectrograph for imaging at visible wavelengths. OSCA provides a selection of 10 different occulting masks with sizes of 0.25 - 2.0 arcseconds in diameter,including two with novel gaussian profiles. There is also a choice of two different sized Lyot stops (pupil plane masks). A dichroic placed before the AO system can give improved suppression performance when occulting masks larger than the seeing disk are used. Also presented are results from observing time with the OSCA system, which highlight the challenges faced by astronomers to obtain high contrast, high resolution images from ground based telescopes. At a time during which there is much activity towards terrestrial planet finding, questions as to the system requirements required for such a task are discussed.

The PSF for astronomical telescopes and instruments depends not only on geometric wavefront aberrations, but also on those polarization aberrations from the polarization properties of reflecting and transmitting surfaces. The image plane irradiance distribution is the linear superposition of four PSF images: one for each of the two orthogonal polarizations and one for each of two cross-coupled polarization terms.

The Keck Planet Imager and Characterizer (KPIC) is a cost-effective upgrade path to the W.M. Keck observatory (WMKO) adaptive optics (AO) system, building on the lessons learned from first and second-generation extreme AO (ExA0) coronagraphs. KPIC will explore new scientific niches in exoplanet science, while maturing critical technologies and systems for future ground-based (TMT, FELT, GMT) and space-based planet imagers (HabEx, LUVOIR). The advent of fast low-noise IR cameras (IR-APD, MKIDS, electron injectors), the rapid maturing of efficient wavefront sensing (WFS) techniques (Pyramid, Zernike), small inner working angle (IWA) coronagraphs (e.g., vortex) and associated low-order wavefront sensors (LOWFS), as well as recent breakthroughs in high contrast high resolution spectroscopy, open new direct exoplanet exploration avenues that are complementary to planet imagers such as VLT-SPHERE and the Gemini Planet Imager (GPI). For instance, the search and detailed characterization of planetary systems on solar-system scales around late-type stars, mostly beyond SPHERE and GPI's reaches, can be initiated now at WMKO.

Complex-mask coronagraphs destructively interfere unwanted starlight with itself to enable direct imaging of exoplanets. This is accomplished using a focal plane mask (FPM); a FPM can be a simple occulter mask, or in the case of a complex-mask, is a multi-zoned device designed to phase-shift starlight over multiple wavelengths to create a deep achromatic null in the stellar point spread function. Creating these masks requires microfabrication techniques, yet many such methods remain largely unexplored in this context. We explore methods of fabrication of complex FPMs for a Phased-Induced Amplitude Apodization Complex-Mask Coronagraph (PIAACMC). Previous FPM fabrication efforts for PIAACMC have concentrated on mask manufacturability while modeling science yield, as well as assessing broadband wavelength operation. Moreover current fabrication efforts are concentrated on assessing coronagraph performance given a single approach. We present FPMs fabricated using several process paths, including deep reactive ion etching and focused ion beam etching using a silicon substrate. The characteristic size of the mask features is 5 mu m with depths ranging over 1 mu m. The masks are characterized for manufacturing quality using an optical interferometer and a scanning electron microscope. Initial testing is performed at the Subaru Extreme Adaptive Optics testbed, providing a baseline for future experiments to determine and improve coronagraph performance within fabrication tolerances.

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument relies on a technique known as the asymmetric pupil Fourier wavefront sensor (APF-WFS) to compensate for the non-common path error that affects the performance of high contrast imaging instruments. The APF-WFS is a powerful tool that senses the wavefront at the level of the science detector, and leads to unbiased wavefront estimates. This paper presents the latest status, linearity properties and reports on the on-sky performance of this sensor, as it is implemented on SCExAO, used to control low-order Zernike modes in a close-loop system.

The Phase Induced Amplitude Apodization Complex Mask Coronagraph (PIAACMC) is an architecture for directly observing extrasolar planets, and can achieve performance near the theoretical limits for any direct-detection instrument. The PIAACMC architecture includes aspheric PIAA optics, and a complex phase-shifting focal plane mask that provides a pi phase shift to a portion of the on-axis starlight. The phase-shifted starlight is forced to interfere destructively with the un-shifted starlight, causing the starlight to be eliminated, and allowing a region for high-contrast imaging near the star. The PIAACMC architecture can be designed for segmented and obscured apertures, so it is particularly well suited for ground-based observing with the next generation of large telescopes. There will be unique scientific opportunities for directly observing Earth-like planets around nearby low-mass stars. We will discuss design strategies for adapting PIAACMC for the next generation of large ground-based telescopes, and present progress on the development of the focal plane mask technology. We also present simulations of wavefront control with PIAACMC, and suggest directions to apply the coronagraph architecture to future telescopes.

Cette thèse s'inscrit dans le contexte de la détection directe de planètes extra-solaires avec les futures très grand télescopes au sol (30 à 42 mètres de diamètre). Les contrastes requis pour une telle détection nécessitent l'utilisation de système d'optique adaptative pour corriger les effets de la turbulence atmosphérique et de coronographes stellaires pour atténuer le flux de l'étoile dans lequel le signal de la planète est noyé. Le but de cette étude est donc d'optimiser, de comparer et de sélectionner les concepts de coronographes stellaires les plus adaptés aux contraintes imposées par ces futurs télescopes (obstruction centrale et segmentation du miroir primaire, support du secondaire. . . ) et cela à différents niveaux de contraste (après correction de la turbulence par une optique adaptative, et après calibration des aberrations statiques du halo par un système d'imagerie différentiel). Enfin, le développement de différents prototypes de coronographes pour êtres testés sur un banc d'optique adaptative est détaillé ainsi que le développement d'une nouvelle technique pour la réalisation d'apodizers (composants critiques pour un certain nombre de coronographes)
This thesis was realized in the context of exoplanet direct detection with ground-based extremely large telescopes (30 to 42 meter diameter). To deliver such contrast level, adaptive/optics System (to correct for the turbulence aberrations) and coronagraphs (to reduce the flux of the parent star where the planet signal is hidden) are required. The intent of this study is to optimize, compare and select optimal coronagraph concepts that can accommodate such telescope constraints (primary mirror obscuration and segmentation, secondary holder. . . ) at several contrast levels (after correction of the atmospheric turbulence with an adaptive optics System, and when a calibration of the halo is performed by the use of a differential imaging System). Finally, prototyping details are described for several coronagraphs that will be implemented on an adaptive optics testbench, as well as the development of a new technical solution for the manufacture of apodizers (critical components for several coronagraph concepts)

For several years, we have been developing vortex phase masks based on sub-wavelength gratings, known as Annular Groove Phase Masks. Etched onto diamond substrates, these AGPMs are currently designed to be used in the thermal infrared (ranging from 3 to 13 pm). Our AGPMs were first installed on VLT/NACO and VLT/VISIR in 2012, followed by LBT/LMIRCam in 2013 and Keck/NIRC2 in 2015. In this paper, we review the development, commissioning, on-sky performance, and early scientific results of these new coronagraphic modes and report on the lessons learned. We conclude with perspectives for future developments and applications.

This thesis follows an investigation into the effects of radiation damage on the e2v CCD201-20; the detector baselined for use in the WFIRST coronagraph imaging and spectroscopy camera systems (hereafter, WFIRST CGI). The CCD201 is an EM-CCD, a variant of traditional CCD technology that is well suited for operation in light starved conditions. Despite successful implementation on many ground-based instruments, the technology has yet to be used within a space environment and therefore has low technological maturity compared to the standard CCD counterpart. Improvement of the technological maturity rested upon in-depth investigations into the effect of radiation damage on the CCD201, which in turn could be used to estimate the End Of Life (EOL) performance of the instrument and de-risk the utilisation of EM-CCDs for the mission. An in-depth radiation campaign was completed whereby multiple CCD201s were irradiated to multiple fluence levels at both room temperature and the nominal operating temperature of the mission (165 K). Performance was measured prior to and following each irradiation, including measurements of low-signal Charge Transfer Inefficiency (CTI), dark current and Clock Induced Charge (CIC). Significant performance differences were noted between the room temperature and cryogenic irradiation case, indicating that cryogenic irradiations are instrumental to accurate EOL performance estimates. CTI was identified as the key limitation to CGI science performance, and so attention then turned to amelioration strategies focused on improving performance in the presence of radiation damage, including trap pumping and narrow-channel modelling. The results presented in this thesis have helped lead to the adoption of the CCD201-20 for the WFIRST mission, have provided key insight into the differences between room temperature and cryogenic irradiations, have advanced the “trap pumping” technique for use on EM-CCDs and presented the properties on the dominant traps that impact CTI for radiation damaged CCDs. The findings are not only useful for the WFIRST CGI, but for any future space mission that will utilise EM-CCD technology in an environment where radiation has the potential to degrade science performance.

We report on the performance of a vector apodizing phase plate coronagraph that operates over a wavelength range of 2-5 mu m. and is installed in MagAO/Clio2 at the 6.5 m Magellan Clay telescope at Las Campanas Observatory, Chile. The coronagraph manipulates the phase in the pupil to produce three beams yielding two coronagraphic point-spread functions (PSFs) and one faint leakage PSF. The phase pattern is imposed through the inherently achromatic geometric phase, enabled by liquid crystal technology and polarization techniques. The coronagraphic optic is manufactured using a direct-write technique for precise control of the liquid crystal pattern. and multitwist retarders for achromatization. By integrating a linear phase ramp to the coronagraphic phase pattern, two separated coronagraphic PSFs are created with a single pupil-plane optic, which makes it robust and easy to install in existing telescopes. The two coronagraphic PSFs contain a 180 degrees dark hole on each side of a star, and these complementary copies of the star are used to correct the seeing halo close to the star. To characterize the coronagraph, we collected a data set of a bright (m(L) = 0-1) nearby star with similar to 1.5 hr of observing time. By rotating and optimally scaling one PSF. and subtracting it from the other PSF, we see a contrast improvement by 1.46 magnitudes at 3.5 lambda/D. With regular angular differential imaging at 3.9 mu m, the MagAO vector apodizing phase plate coronagraph delivers a 5 sigma Delta mag contrast of 8.3 (= 10(-3.3)) at 2 lambda/D and 12.2 (= 10(-4.8)) at 3.5 lambda/D.

Diamond is a material with many exceptional properties. In this thesis methods for fabrication of microstructures as well as several applications of such structures in optics, microfluidics and electrochemistry are presented. A method for etching deep and highly precise gratings is described. This method was used to fabricate circularly symmetric half wave plates for use in vector vortex coronagraphs. Such coronagraphs are a very promising approach to the direct imaging of extrasolar planets. By varying the lateral etch rate of the aluminum mask during diamond etching in an inductively coupled plasma, the sidewall angle of the etched structures could be controlled. This method was used to make smooth sloped sides on a waveguide for coupling light into it. Antireflective structures that drastically reduced the surface reflection in a wavelength band between 10 and 50 µm were also fabricated. An array of boron doped diamond microelectrodes for electrochemical measurements in a microchannel was fabricated and tested, showing very good stability and reusability. Several hundred hours of use did not adversely affect their performance and no damage to them could be detected by atomic force microscopy or scanning electron microscopy. Superhydrophobic surfaces in diamond were demonstrated, using both hydrogen and fluorine termination. Hydrogen termination on a flat surface gives contact angles below 90°. To achieve a superhydrophobic surface with this low intrinsic hydrophobicity, structures looking like microscopic nail heads were fabricated. The effect of water pressure on immersed superhydrophobic surfaces was also studied and it was found that the collapse of the superhydrophobic state due to pressure was sometimes reversible as the pressure was lowered. Finally, a method was tested for functionalizing diamond surfaces using block copolymers of polyethylene oxide and polypropylene oxide to both passivate the surface and to attach synthetic binder molecules. This method was found to give very high signal to noise ratios when detecting C-reactive protein.

SHARK-NIR is the second-generation high-contrast coronagraphic imager for the Large Binocular Telescope (LBT). In my Ph.D. project I have been involved in the conceptual and final design phase of the instrument. In specific, I developed a simulator in IDL language that operated as a virtual test bench to make a comparative study of several coronagraphic techniques identified as suitable candidates for implementation in the instrument. The simulator is based on physical optics propagation and adopts an end-to-end approach to generate images in presence of several sources of optical aberrations, from atmospheric residuals to telescope vibrations and non common path aberrations (NCPA). In particular, a big effort has been devoted to the optimization of the software efficiency through a dedicated parallelization scheme, to modelling of NCPA spatial and temporal properties, to the investigation of the effects of telescope vibrations and of the impact of the forthcoming upgrade of LBT Adaptive Optics system. I explored the coronagraphic performance in a wide range of observing conditions and characterized the coronagraphs sensitivity to aberrations, misalignments of optical components and chromatism. I also helped developing a data reduction pipeline to process simulated data adopting several algorithms. Simulations results have been used to define a final set of coronagrahic solutions that allow to fulfill the top-level scientific requirements.\\Finally, I validated with simulations the phase diversity approach as a strategy for on-line sensing of NCPA. Simulations contributed to the final choice of the internal DM for both NCPA and fast tip-tilt correction.
SHARK-NIR è l'imager ad alto contrasto di seconda generazione per il Large Binocular Telescope. Durante il mio Ph.D. sono stato coinvolto nella fasi di design concettuale e finale dello strumento. In specifico, ho sviluppato un simulatore in IDL che è stato utilizzato come banco di test virtuale per realizzare uno studio comparativo di diverse tecniche coronografiche identificate come possibili candidate a essere implementate nello strumento. Il simulatore è basato sulla propagazione di fronti d'onda e utilizza un approccio end-to-end per generare immagini in presenza di svariate sorgenti di aberrazioni ottiche, da residui atmosferici a vibrazioni e aberrazioni di non-common path (NCPA). Un'attenzione particolare è stata rivolta all'ottimizzazione del software attraverso specifici schemi di parallelizzazione, alla modellizzazione delle proprietà temporali e spaziali delle NCPA e allo studio dell'impatto del prossimo upgrade dei sistema di Ottica Adattiva di LBT. Ho esplorato le performance di diversi coronografi in un ampio range di condizioni osservative e caratterizzato la loro sensibilità ad aberrazioni, disallineamenti e cromatismo. Ho anche contribuito allo sviluppo di una pipeline di riduzione dati rivolta a processare le immagini simulate adottando diversi algoritmi. I risultati delle simulazioni sono stati utilizzati per effettuare una selezione di tecniche coronografiche in grado di soddisfare i requisiti scientifici dello strumento. Infine, ho validato attraverso simulazioni un approccio denominato Phase Diversity il cui fine è misurare on-line le NCPA. Le simulazioni hanno contribuito alla scelta di implementare uno specchio deformabile interno per la correzione simultanea di NCPA e vibrazioni residue ad alta frequenza.

HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a new image of the third inner disk component of HD 141569 A made in the L' band (3.8 mu m) during the commissioning of the vector vortex coronagraph that has recently been installed in the near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory Keck II adaptive optics system. We used reference point-spread function subtraction, which reveals the innermost disk component from the inner working distance of similar or equal to 23 au and up to similar or equal to 70 au. The spatial scale of our detection roughly corresponds to the optical and near-infrared scattered light, thermal Q, N, and 8.6 mu m PAH emission reported earlier. We also see an outward progression in dust location from the L' band to the H band (Very Large Telescope/SPHERE image) to the visible (Hubble Space Telescope (HST)/STIS image), which is likely indicative of dust blowout. The warm disk component is nested deep inside the two outer belts imaged by HST-NICMOS in 1999 (at 406 and 245 au, respectively). We fit our new L'-band image and spectral energy distribution of HD 141569 A with the radiative transfer code MCFOST. Our best-fit models favor pure olivine grains and are consistent with the composition of the outer belts. While our image shows a putative very faint point-like clump or source embedded in the inner disk, we did not detect any true companion within the gap between the inner disk and the first outer ring, at a sensitivity of a few Jupiter masses.

Artifacts in polarimeters are apparent polarization features which are not real but result from the systematic errors in the polarimeter. The polarization artifacts are different between division of focal plane, spectral, and time modulation polarimeters. Artifacts result from many sources such as source properties, micropolarizer arrays, coatings issues, vibrations, and stress birefringence. A modeling examples of polarization artifacts due to a micro-polarizer array polarimeter is presented.

The search for life on other worlds is an exciting scientific endeavor that could change the way we perceive our place in the universe. Thousands of extrasolar planets have been discovered using indirect detection techniques. One of the most promising methods for discovering new exoplanets and searching for life is direct imaging with a coronagraph. Exoplanet coronagraphy of Earth-like planets is a challenging task, but we have developed many of the tools necessary to make it feasible. The Phase-Induced Amplitude Apodization (PIAA) Coronagraph is one of the highest-performing architectures for direct exoplanet imaging. With a complex phase-shifting focal plane mask, the PIAA Complex Mask Coronagraph (PIAACMC) can approach the theoretical performance limit for any direct detection technique. The architecture design is flexible enough to be applied to any arbitrary aperture shape, including segmented and obscured apertures. This is an important feature for compatibility with next-generation ground and space-based telescopes. PIAA and PIAACMC focal plane masks have been demonstrated in monochromatic light. An important next step for high-performance coronagraphy is the development of broadband phase-shifting focal plane masks. In this dissertation, we present an algorithm for designing the PIAA and PIAACMC focal plane masks to operate in broadband. We also demonstrate manufacturing of the focal plane masks, and show laboratory results. We use simulations to show the potential performance of the coronagraph system, and the use of wavefront control to correct for mask manufacturing errors. Given the laboratory results and simulations, we show new areas of exoplanet science that can potentially be explored using coronagraph technology. The main conclusion of this dissertation is that we now have the tools required to design and manufacture PIAA and PIAACMC achromatic focal plane masks. These tools can be applied to current and future telescope systems to enable new discoveries in exoplanet science.

O objetivo do trabalho da Dissertação é estudar distúrbios solar-interplanetário-geomagnéticos, como ejeções de massa coronais solares (Coronal Mass Ejections - CMEs) usando observações de coronógrafos de luz branca e de raios cósmicos de alta energia (muons). A partir de imagens do coronógrafo LASCO-C3 (Large Angle and Spectroscopic Coronagraph), ejeções coronais de massa (CMEs) foram segmentadas de forma supervisionada por textura. O contorno identificado foi utilizado para estimar velocidades radiais e de expansão de um conjunto de 57 CMEs associadas a eventos solares próximos ao limbo. Optou-se por segmentação por textura, buscando-se parametrizar estimativas de velocidades de CME que não são consenso. De forma geral o contorno identificado pela técnica mostrou-se coerente com a definição de CME e a posição angular, velocidade radial e de expansão estimadas são similares aos resultados anteriores obtidos por catálogos produzidos manualmente. Por outro lado, usando dados de raios cósmicos de alta energia (muons), assinaturas precedentes a chegada da massa de plasma solar foram estudadas usando dados da Rede Mundial de Detectores de Muons (GMDN). Foi elaborada e estudada a distribuição da intensidade de raios cósmicos como função do ângulo de pitch para períodos associados às 16 tempestades geomagnéticas fracas ou moderadas observadas em 2008. Em 14 dos eventos foram observados possíveis precursores, tanto acréscimos como decréscimos sistemáticos. Não há razão identificada para a ausência de precursores nos dois eventos restantes.
The objective of this work is to study solar-interplanetary-geomagnetic disturbances like coronal mass ejections (CMEs) using observations from the white light coronagraph and high-energy cosmic ray (muons). Images from the Large Angle and Spectroscopic Coronagraph (LASCO-C3) were segmented by texture in a supervised way and the identified contour was used to estimate the radial and expansion speed of a set of 57 limb CMEs for the period between 1997 and 2001. Texture analysis was chosen in a way to parameterize the estimation of CMEs contours, which are not always consensus. In a general view, the identified contour is in agreement with the CME definition and the estimate position angle, radial speed and expansion speed are in agreement with previous catalogs manually done. In the other hand, using high-energy cosmic ray (muons) observations, signatures preceding the arrival of plasma structures were studied using data from the Global Muon Detector Network (GMDN). Pitch angle distributions were done for periods associated with the 16 small and moderate geomagnetic storms observed in 2008. Fourteen of them show some possible precursors, both precursory increases and precursory decreases. No clear reason was found yet for not seeing precursors in the remaining two events.

This Thesis aims to study coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) using remove sensing observations from the solar corona, interplanetary in situ data and observations from ground-based cosmic ray detectors. CMEs have a central role on the Sun-Earth relationships because they are one of the main sources of geomagnetic disturbances. We have started the analysis by using a list of magnetic clouds (MCs) observed in the Earth-vicinity from 2008 to 2011. After probing the interplanetary structure, we identified the CMEs ejected in appropriate time and direction to produce each magnetic cloud. The CME propagation directions were studied thanks to the simultaneous observations of the solar corona from three viewpoints: one from the LASCO (Large Angle and Spectroscopic Coronagraph) and two others from SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation). We developed a new methodology to track the CMEs in 3D combining pseudo-automatic tracking by texture with triangulation and tie-pointing analysis. For each CME analyzed, we estimated the tridimensional speed (magnitude and direction) using the new method and compared the results with previous works. Combining observations of four ground-based cosmic ray (muon) detectors, we deduced the cosmic ray density gradient during each magnetic cloud period and the overall position of the MC center. In some cases, we fit a model of cosmic ray distribution inside magnetic clouds to the observed data and deduced further properties of the MCs, such as orientation and diameter. Finally, for each case, the results derived in the solar corona were compared with those derived from cosmic ray observations.
O objetivo desta Tese é estudar ejeções coronais de massa (conhecidas pela sigla CME, da expressão em Língua Inglesa, coronal mass ejections) e suas correspondentes estruturas interplanetárias usando observações de sensoriamento remoto da coroa solar, dados de campo magnético e plasma in situ do meio interplanetário e observações de detectores de raios cósmicos instalados na superfície da Terra. As CMEs têm um papel central na relação Sol-Terra porque elas são uma das principais causadoras de tempestades geomagnéticas. Iniciou-se a análise desta Tese a partir de uma lista de nuvens magnéticas observadas entre 2008 e 2011 nas vizinhanças da Terra. Uma vez caracterizadas as estruturas interplanetárias, identificaram-se as CMEs ejetadas no período e direção apropriados para produzir cada uma das nuvens magnéticas. A direção das CMEs pode ser estudada graças a observação simultânea da coroa solar a partir de três pontos de observação distintos: um proveniente do instrumento LASCO (\emph{Large Angle and Spectroscopic Coronagraph}) e outros dois do SECCHI (\emph{Sun Earth Connection Coronal and Heliospheric Investigation}). Desenvolveu-se um novo método para rastrear as CMEs em três dimensões usando o rastreio pseudo-automático por textura, triangulação e pontos de amarra. Para cada CMEs, estimou-se a velocidade tridimensional (tanto a magnitude como a direção) usando o novo método e, nos casos já abordados em trabalhos anteriores, compararam-se os resultados. Por outro lado, combinando-se observações de quatro detectores de raios cósmicos (múons), deduziu-se o gradiente da densidade dos raios cósmicos para todos os casos de nuvens magnéticas observadas e, por conseguinte, estimou-se a sua posição geral. Em alguns casos, ajustou-se um modelo da distribuição dos raios cósmicos no interior da nuvem magnética com os dados observados e deduziram-se outras propriedades da nuvem magnética, como orientação e diâmetro. Finalmente, para cada caso, resultados obtidos na coroa solar foram comparados com aqueles deduzidos por observações de raios cósmicos.

On March 2015 an L'-band vortex coronagraph based on an Annular Groove Phase Mask made up of a diamond sub-wavelength grating was installed on NIRC2 as a demonstration project. This vortex coronagraph operates in the L' band not only in order to take advantage from the favorable star/planet contrast ratio when observing beyond the K band, but also to exploit the fact that the Keck II Adaptive Optics (AO) system delivers nearly extreme adaptive optics image quality (Strehl ratios values near 90%) at 3.7 mu m. We describe the hardware installation of the vortex phase mask during a routine NIRC2 service mission. The success of the project depends on extensive software development which has allowed the achievement of exquisite real-time pointing control as well as further contrast improvements by using speckle nulling to mitigate the effect of static speckles. First light of the new coronagraphic mode was on June 2015 with already very good initial results. Subsequent commissioning nights were interlaced with science nights by members of the VORTEX team with their respective scientific programs. The new capability and excellent results so far have motivated the VORTEX team and the Keck Science Steering Committee (KSSC) to offer the new mode in shared risk mode for 2016B.

Úkolem této práce je vytvoření adaptivního filtru pro vizualizaci CME v obrazech z kosmického koronografu, jejich implementování a výsledné testování na datech z kosmické sondy SOHO. V práci je zahrnuta potřebná teorie z oblasti astronomie a matematiky, popis NRGF, navrhnuté úpravy tohoto filtru a je přiložen program, který sloužil k jejich otestování.

SCExAO is the premier high-contrast imaging platform for the Subaru Telescope. It offers high Strehl ratios at near-IR wavelengths (y-K band) with stable pointing and coronagraphs with extremely small inner working angles, optimized for imaging faint companions very close to the host. In the visible, it has several interferometric imagers which offer polarimetric and spectroscopic capabilities. A recent addition is the RHEA spectrograph enabling spatially resolved high resolution spectroscopy of the surfaces of giant stars, for example. New capabilities on the horizon include post-coronagraphic spectroscopy, spectral differential imaging, nulling interferometry as well as an integral field spectrograph and an MKID array. Here we present the new modules of SCExAO, give an overview of the current commissioning status of each of the modules and present preliminary results.

La future mission PROBA-3 de l'ESA démontrera le vol en formation de satellites. Elle emportera à son bord le coronographe solaire géant ASPIICS. Un satellite portera un disque de 1,42m de diamètre afin d'occulter le Soleil. Un second satellite embarquera un coronographe de Lyot et se positionnera dans l'ombre du premier à 150m, avec une précision millimétrique. ASPIICS observera la région interne de la couronne du Soleil entre 1,1 et 3,0 rayons solaires, qui reste relativement inexplorée. La brillance de la couronne y est très peu intense, de six à dix ordres de grandeur plus faible que celle du disque solaire. Pour un tel instrument, la diffraction de la lumière du Soleil apparait donc comme un facteur clé. De plus, les contraintes associées au vol en formation sont nouvelles et doivent être étudiées.Cette thèse souhaite répondre à cette problématique une approche numérique. Dans un premier temps, la diffraction par l'occulteur est calculée par des modèles dimensionnés pour le cas d'étude. L'intensité de l'ombre résulte d'une somme incohérente sur le disque solaire. Ensuite, la propagation de Fresnel de l'onde solaire diffractée dans le coronagraphe est modélisée suivant le formalisme de l'optique de Fourier. La simulation utilise des algorithmes FFT avec des tableaux de grandes tailles. Enfin, l'erreur de front d'onde due aux défauts de surface du télescope, et le désalignement et dépointage de la paire de satellites sont implémentés. Le résultat final est donné par la distribution spatiale de l'intensité de la diffraction au niveau du détecteur. L'impact de la taille du masque et du stop de Lyot ainsi que des effets de vignettages sont également analysés.Cette étude démontre que les occulteurs en dent de scie sont meilleurs que le disque simple quant à la profondeur de l'ombre, et presque aussi bons que le disque apodisé. Dans le coronagraphe, l'intensité de la diffraction reste comparable à la brillance de la couronne solaire à 1,1 rayon solaire, mais elle est fortement réduite à partir de 1,3 rayons solaires. Ceci permet l'observation de la couronne solaire. Tandis que les erreurs de vol en formation ont un impact limité, les effets de diffusion dégradent grandement la performance. Les résultats de cette thèse ont participé au dimensionnement de ASPIICS
The future formation flying PROBA-3 ESA mission will fly the giant solar coronagraph ASPIICS. One spacecraft will carry an occulter disc of 1.42m diameter in front of the Sun. It will cast its shadow onto the 5cm aperture of a Lyot-style coronagraph on-board a second spacecraft that will be positioned 150m behind with millimeters accuracy. ASPIICS aims to observe the solar corona in the rather unexplored region from 1.1 to 3.0 solar radii, where the coronal brightness is six to ten orders of magnitude lower than the solar disc. For such high-contrast instrument, straylight from sunlight diffraction is a key driver for the performance. Dedicated and accurate modeling of these diffraction effects are thus required. Additionally, the novel concept of formation flying brings new constraints to be investigated.This thesis aims to meet these needs. The method is numerical. First, the diffraction from the occulter is calculated by models designed for the study case. The umbra is computed as an incoherent summation over the solar disc. Second, the Fresnel propagation of the diffracted wave front through the coronagraph is built upon Fourier optics, and uses 2D FFT with large arrays. Perturbations are finally added to the model, like roughness scattering from the telescope, or misalignment and off-pointing of the spacecraft flying formation. The end result is the spatial distribution of the diffracted sunlight intensity at detector level. Sizing the Lyot mask and stop and vignetting effects are also analyzed.Regarding the umbra intensity, the study shows that serrated occulters are better than the simple disc and can almost reach the straylight performance of the apodized disc. At detector level, the brightness of the diffraction at 1.1 solar radius remains similar to the corona. But the coronagraph manages to reduce the straylight to the required level beyond 1.3 solar radius. While the formation flying errors have a limited impact, the scattering significantly increases the diffraction in the outer field-of-view. These results have been used to support the design of ASPIICS

La couronne solaire est la partie de l'atmosphère du Soleil qui s'étend de la photosphère (surface solaire d'où sont émis les photons) jusque dans le milieu interplanétaire. Sa compréhension relève d'un enjeu majeur car elle est à l'origine de phénomènes qui peuvent perturber les télécommunications, les êtres vivants et même le climat. L'instrument privilégié pour l'observer est le coronographe, système optique occultant le disque solaire au profit de la couronne, un million de fois moins intense. Ma thèse porte sur son étude, en particulier à travers les projets spatiaux :- SOLAR ORBITER, qui doit s'approcher du Soleil à 0.2 unité astronomique (distance Terre-Soleil), permettant ainsi une très haute résolution spatiale ;- SMESE, en coopération avec la Chine, qui étudiera la couronne dans l'infrarouge lointain ;- et ASPIICS, dont l'occulteur externe sera placé à 150 m de l'instrument imageur, permettant d'observer la couronne dans des conditions proches d'une éclipse solaire naturelle.Le premier aspect abordé est la réjection de la lumière parasite instrumentale, dont l'optimisation est une des problématiques majeures en coronographie. Le second concerne les modes d'observation par imagerie en lumière blanche, imagerie monochromatique, et interférométrie, en particulier le Fabry Perot. Le développement et l'amélioration de ces techniques permettra des avancées considérables en terme de résolution et l'accès à la couronne toujours plus proche de la surface du Soleil, lieu encore mal connu où l'activité solaire prend naissance
The solar corona is the part of the Sun's atmosphere that extends from the photosphere (solar surface where the photons are emitted) into the interplanetary medium. Its understanding is a major issue because it is the source of phenomena that can disrupt telecommunications, living beings and even climate. The most appropriate tool to observe it is the coronagraph, an optical system obscuring the solar disk in favor of the corona, a million times fainter. My thesis deals with its review, particularly through the spaceprojects :- Solar Orbiter, which will approach the Sun at 0.2 astronomical unit (distance between Earth and Sun), allowing a very high spatial resolution ;- SMESE, in cooperation with China, which should study the corona in the Lymanalpha (and far infrared) ;- and ASPIICS, which will observe the corona in conditions close to a natural solar eclipse, with its occulting disk located at 150 m from the imaging instrument.The first point tackled is the rejection of instrumental stray light, whose optimization is one of the major problems in coronagraphy. The second concerns the methods of observation and imaging in white light, monochromatic imaging, and interferometry, in particular the Fabry Perot. The development and improvement of these techniques will allow considerable progress in terms of resolution and access to the corona ever closer to the Sun's surface, the location yet little known where the solar activity originates

L’imagerie d’exoplanètes est limitée par deux obstacles intrinsèques : le faible écart angulaire entre planète et étoile, et le très faible flux lumineux en provenance de la planète par rapport à la lumière de l’étoile. Le premier obstacle est surmonté par l’utilisation de très grands télescopes, de la classe des dix mètres de diamètre, et éventuellement depuis le sol de systèmes d’optique adaptative, qui permettent d’atteindre de hautes résolutions angulaires. Le deuxième obstacle est surmonté par l’utilisation de coronographes. Les coronographes sont des instruments conçus pour filtrer la lumière de l’étoile tout en laissant passer la lumière de l’environnement circumstellaire. Cependant, toute aberration optique en amont du coronographe engendre des fuites de lumière stellaire à travers le coronographe. Ces fuites se traduisent par un fouillis de tavelures dans les images scientifiques, tavelures qui cachent d’éventuelles planètes. Il est donc nécessaire de mesurer et de corriger les aberrations quasi-statiques à l’origine des tavelures. Cette thèse présente des contributions théoriques, numériques et expérimentales à la mesure et à la correction des aberrations des imageurs coronographiques. La première partie décrit le contexte et présente la méthode de la diversité de phase coronographique, un formalisme qui considère l’analyse de surface d’onde post-coronographique comme un problème inverse posé dans un cadre bayésien. La deuxième partie concerne l’imagerie depuis le sol. Elle présente tout d’abord une expression analytique permettant de modéliser l’imagerie coronographique en présence de turbulence, puis l’extension de la méthode de diversité de phase coronographique à la mesure depuis les télescopes au sol donc en présence de turbulence résiduelle, et enfin une validation en laboratoire de cette méthode étendue. La troisième partie est consacrée aux futurs imageurs spatiaux à très hauts contrastes pour lesquels il faut corriger non pas seulement la phase mais tout le champ complexe. Elle présente la validation en laboratoire de la mesure d’un champ complexe d’aberrations par diversité de phase coronographique, ainsi que des premiers résultats d’extinction de la lumière en plan focal par une méthode non linéaire, le non-linear dark hole
Exoplanet imaging has two intrinsic limitations, namely the small angular separation between the star and the planet, and the very low light flux from the planet compared to the starlight. The first limitation is overcome by using very large telescopes of the ten-metre diameter class, and, for ground-based telescopes, adaptive optics systems, which allow high angular resolution imaging. The second limitation is overcome by using a coronagraph. Coronagraphs are optical devices which filter the starlight while granting passage to the light coming from the stellar environment. However, any optical aberration upstream of the coronagraph causes some of the starlight to leak through the coronagraph. This unfiltered starlight in turn causes speckles in the scientific images, and the light of the planets that could be there is lost among the speckles. Consequently, measurement and correction of the quasi-static aberration which generate the speckles are necessary for the exoplanet imagers to achieve their full potential. This thesis introduces theoretical, numerical, and experimental contributions to the topic of measurement and correction of the aberrations in coronagraphic imagers. The first part describes the context and introduces coronagraphic phase diversity, which is a Bayesian inverse problem formalism for post-coronagraphic wave-front sensing. The second part is focused on ground-based imaging. It introduces an analytic expression for coronagraphic imaging through turbulence, the extension of coronagraphic phase diversity to on-sky measurement through residual turbulence, and a laboratory validation of the extended method. The third part is concerned with future high-contrast space-based imagers, which will require not only phase correction, but a full complex wave-front correction. It presents the laboratory validation of coronagraphic phase diversity as a post-coronagraphic complex wave-front sensor, and first results of active contrast enhancement in the focal plane through thecreation of a non-linear dark hole

Optical vortices represent a particular class of wavefront dislocations characterized by a topological charge l. The surface of constant phase of an electromagnetic wave carrying an optical vortex has a helical structure and presents a singularity along the axis of the helicoid, where the phase is undefined. As a consequence, the intensity distribution of a vortex light beam contains a central dark region, where the intensity is zero due to destructive interference. Optical vortices can be produced by using phase modifying devices, i.e. particular optical elements possessing an optical singularity generally located at their center. The most efficient of them are fork holograms and spiral phase plates. In the last decade, the properties of optical vortices have found interesting applications in optical physics. Among these, the most promising are those in optical communications, nanotechnologies and biology. Optical vortices are attracting increasing attention also in astronomy, where the properties of such features of the electromagnetic radiation could provide a new approach to the study of astrophysical phenomena. The purpose of this Thesis is to present some possible applications of optical vortices to instrumental astronomy. In particular, this work is focused on the development and testing of new techniques to improve the performances of optical systems. Firstly, a method is proposed to improve the resolving power of a diffraction-limited telescope by means of an l = 1 fork hologram. Both the experiments and numerical simulations reveal that the superposition of the optical vortices produced by two light beams characterized by equal Airy intensity distributions present a detectable asymmetry even for separations that are one order of magnitude below the limit of the Rayleigh criterion. It is shown that this result can be achieved both with monochromatic and white light beams. We then present the first astronomical experiment in which we produced optical vortices in starlight beams with an l = 1 fork hologram placed at the focal plane of the Galileo 122 cm telescope in Asiago. By using the Lucky Imaging approach to reduce the effects of mediocre seeing conditions, we were able to observe the images of the optical vortices produced by the two main components of the multiple system alpha Her, in non-monochromatic light, and by the single star alpha Boo, using a narrow bandpass. In both cases, the intensity profiles of the observed optical vortices are in agreement with numerical simulations. Detailed analytical models and numerical simulations confirm that the spatial structure of an optical vortex produced by a phase modifying device is extremely sensitive to off-axis displacements of the input beam, especially when high values of the topological charge l are used. This property could be used to perform ground-based astrometric measurements with a precision competitive to standard PSF-fitting astrometry. The sensitivity to small off-axis displacements might also help to improve the tip/tilt correction of the wavefront for a small field of view. We discuss also the possible application of the nulling property of even-charged optical vortices to perform high-contrast coronagraphy. In this case, the nulling of the light of an on-axis star is achieved by using a spiral phase plate and a circular diaphragm as Lyot stop. In principle, this coronagraphic design is one of the very few that might allow direct imaging of extrasolar terrestrial planets. However, such remarkable performance is still strongly limited by the current techniques used to manufacture spiral phase plates. In the framework of projecting an l = 2 optical vortex coronagraph for visible wavelengths, we present the results of numerical simulations obtained considering a spiral phase plate with a surface subdivided in N discrete levels. A description of the experimental procedures used to test spiral phase plates manufactured with PMMA (polymethyl methacrylate) material is also given.
I vortici ottici rappresentano una particolare classe di dislocazioni dei fronti d'onda caratterizzate da una carica topologica l. La superficie di fase costante di un'onda elettromagnetica che trasporta un vortice ottico ha una struttura elicoidale. Lungo l'asse di questa elica è presente una singolarità in cui la fase non può essere definita. Di conseguenza, la distribuzione d'intensità di un fascio di luce contenente un vortice ottico presenta una zona centrale dove l'intensità è nulla per effetto dell’interferenza distruttiva. I vortici ottici possono essere prodotti utilizzando particolari elementi ottici detti phase modifying devices che modificano la fase di un'onda incidente. I più efficienti tra questi sono i fork holograms (ologrammi) e le spiral phase plates (maschere di fase). Negli ultimi anni, le proprietà dei vortici ottici hanno trovato interessanti applicazioni nei campi della fisica e dell'ottica. Tra queste, le più promettenti sono quelle in comunicazioni ottiche, nelle nanotecnologie ed in biologia. Recentemente, i vortici ottici stanno suscitando un crescente interesse anche nella comunità astronomica. Infatti, queste particolari proprietà della radiazione elettromagnetica potrebbero permettere di studiare diversi fenomeni astrofisici da un punto di vista completamente nuovo. In questa Tesi vengono presentate alcune possibili applicazioni dei vortici ottici in strumentazione astronomica. In particolare, lo scopo principale di questo lavoro è lo sviluppo di nuove tecniche che permetteranno di migliorare le prestazioni di sistemi ottici. In primo luogo, viene proposto un metodo per aumentare il potere risolutivo di un telescopio limitato dalla diffrazione che prevede l'utilizzo di un fork hologram con una singola dislocazione. I risultati di esperimenti e simulazioni numeriche rivelano che la sovrapposizione dei vortici ottici prodotti da due fasci di luce con una distribuzione d'intensità di Airy mostra già un'evidente asimmetria quando la separazione è di un ordine di grandezza inferiore rispetto al limite posto dal criterio di Rayleigh. Questo risultato è stato ottenuto sia in luce monocromatica, sia in luce bianca. Viene poi presentato il primo esperimento astronomico in cui sono stati prodotti vortici ottici con un fork hologram avente una singola dislocazione posto al piano focale del telescopio Galileo da 122 cm di Asiago. Utilizzando i principi del Lucky Imaging per ridurre gli effetti provocati da condizioni di seeing mediocre, sono state osservate le immagini dei vortici ottici prodotti dalle due componenti principali del sistema multiplo alfa Her, in luce non monocromatica, e dalla stella singola alfa Boo, utilizzando un filtro spaziale a banda stretta. In entrambi i casi, i profili d’intensità dei vortici ottici osservati sono riproducibili con simulazioni numeriche. La sensibilità dell'immagine di un vortice ottico prodotto con un phase modifying device rispetto a spostamenti fuori asse del fascio entrante è confermata da modelli analitici dettagliati e anche da simulazioni numeriche, specialmente nel caso in cui vengano utilizzati elevati valori della cariche topologica l. Questa proprietà potrebbe essere utilizzata per fare misure astrometriche da terra con una precisione che potrebbe competere con quella fornita dalle tecniche standard di astrometria di PSF. La sensibilità rispetto a piccoli spostamenti fuori asse potrebbe anche essere sfruttata per migliorare la correzione dell’aberrazione di tip/tilt del fronte d'onda in un piccolo campo di vista. Viene poi discussa la possibile applicazione di vortici ottici con carica topologica pari nella coronografia ad alto contrasto. In questo caso, l'azione combinata di una spiral phase plate e di un diaframma circolare utilizzato come stop di Lyot permette di annullare totalmente la luce di una stella in asse. Studi teorici indicano che il coronografo a vortici ottici è uno dei pochi che potrebbe realmente permettere l'osservazione diretta di pianeti extrasolari di tipo terrestre. Purtroppo, questa notevole proprietà è fortemente limitata dalle attuali tecniche usate per produrre le spiral phase plate. Nell'ambito di un progetto di costruzione di un coronografo a vortici ottici con l = 2 ottimizzato per lunghezze d'onda visibili, vengono presentati i risultati di simulazioni numeriche ottenuti considerando una spiral phase plate la cui superficie è suddivisa in N livelli discreti. Infine, vengono discusse le procedure sperimentali utilizzate per testare spiral phase plates in PMMA (polimetil-metacrilato).

L'observation directe des exoplanètes est rendue difficile par l'énorme contraste entre la planète et l'étoile autour de laquelle elle gravite, ainsi que la faible séparation angulaire entre ces deux corps. Un tel niveau de contraste aussi proche de l'étoile être atteint en couplant l'imagerie à haute résolution angulaire et la coronographie, qui atténue le flux en provenance de l'étoile ; les performances ultimes d'un instrument d'imagerie à haut contraste sont alors limitées par ses aberrations quasi-statique. Au cours de cette thèse a été conçu un ASO plan focal dédié à la calibration des aberrations quasi-statiques dans les systèmes d'imagerie à haut contraste. Cet ASO, baptisé COFFEE, permet d'estimer les aberrations en amont et en aval du coronographe à partir d'images coronographiques acquises en plan focal différant d'une phase de diversité connue introduite en amont du coronographe. Au cours de cette thèse, COFFEE a été conçu et validé par simulations numérique et démontré expérimentalement sur banc. L'identification de plusieurs facteurs limitant la précision de l'estimation des aberrations a ensuite induit une modification du formalisme sur lequel repose COFFEE pour l'adapter à l'estimation d'aberrations de hautes fréquences spatiales avec une précision nanométrique. Cette version hauts ordres de COFFEE a été utilisée avec succès sur l'instrument SPHERE, où la compensation des aberrations estimées par COFFEE a permis d'optimiser le contraste. Enfin, une nouvelle méthode de compensation a été développée pour permettre d'atteindre de très hauts niveaux de contraste sur le détecteur scientifique
Performing an exoplanet direct detection means being able to image an object as faint as an extra-solar planet very close to its parent star. After compensation of the turbulence by the XAO loop and most of the star light removed by a coronagraph, the ultimate limitation of high contrast imaging systems lies in its quasi-static aberrations that creates a residual signal which limit the achievable contrast on the scientific detector. To increase the achievable contrast on the detector, these aberrations must be compensated for, ideally using focal plane data recorded from the scientific detector to avoid differential aberrations. The aim of this thesis was to develop a focal-plane wavefront sensor (WFS) dedicated to the estimation of quasi-static aberrations in high contrast imaging systems. This WFS, called COFFEE, estimates the aberrations both upstream and downstream of the coronagraph using coronagraphic focal plane images that differ from a known diversity aberrations introduced upstream of the coronagraph. During this research work, COFFEE has been developed, tested using numerical simulations and demonstrated on an in-house bench. Considering the limitations of the estimation accuracy, COFFEE's formalism has then been modified to allow it to estimate high frequencies aberrations with nanometric precision. This extended version of COFFEE has been successfully used on SPHERE to optimize the contrast on the scientific detector of the instrument using COFFEE in a dedicated compensation process. Lastly, a new compensation method has been developed in order to reach very high contrast levels on the scientific detector

L’imagerie à très haute dynamique s’applique à de nombreux domaines de recherche en astronomie et astrophysique. Cette problématique observationnelle est abordée sur plusieurs fronts par de nombreuses techniques complémentaires : coronographie, interferométrie, optique adaptative, controle de front d’onde et discrimination des speckles. La combinaison de celles ci permet d’atteindre un haut contraste avec pour ultime objectif l’imagerie d’exoplanètes et l’étude de l’environnement stellaire. Le travail présenté dans ce manuscrit se focalise sur la coronographie et plus particulièrement sur l’optimisation active du procedé d’occultation en fonction du contexte observationnel.La première partie de cette recherche traite de l’observation d’objets résolus par le développement d’un masque focal de Lyot de diamètre variable. La deuxième partie s’applique à étendre le concept du masque focal adaptatif au masque de phase de type Roddier pour l’observation de l’environnement proche d’objets non résolus. L’utilisation des propriétés des cristaux liquides permet de réaliser un déphasage par rotation de polarisation et une modulation de transmission à l’extérieur du masque. Cette modulation permet un controle actif d’optimisation de l’interférence pour une adéquation du masque au contexte observationnel : longueur d’onde, morphologie d’image et défauts intrinsèques au masque, agitation atmosphérique. La dernière partie de ce manuscrit ébauche de nouvelles perspectives quant à la possibilité d’une imagerie à haut contraste. La modulation temporelle de phase transmise par un masque focal adaptatif est mise à profit par l’utilisation des méthodes de détection synchrone
High contrast imaging of extra-solar planets and environments of bright astro- physical objects in general, such as stars, active galactic nuclei or objects of the Solar System is a challenging task. Different approaches are needed if the bright region to occult is optically resolved or not. We present the Adaptive Mask concept, observations on sky and numerical simulations show the usefulness of the proposed methods to optimize the efficiency of the coronagraphs for optically resolved or non resolved objects. Accessing small IWA is considered as an edge as it provides substantial scientific and technical advantages. One of the difficulties of accessing small IWA is that coronagraphs become very sensitive to low-order aberrations such as tip-tilt. Our original approach aims at integrating the small IWA capability and the mitigation of sensitivity to low-order aberrations within the coronagraph itself. Our concept is applicable to both low and high Strehl regimes, corresponding to current and next generation AO systems. The adaptive coronagraph can adapt dynamically, in quasi real time, to adjust to the observing conditions to deliver a stable and optimized contrast at the science image level. The mask adaptability both in size, phase and amplitude also compensates for manufacturing errors of the mask itself, and potentially for chromatic effects. The mask adaptability concept using a local phase modulation in the focal plane allows synchronous modulation for high dynamic range synchronous detection of a faint target immersed in a background. The coherence of the speckles with the central star is used to discriminate them from proper companions

L'étude des exoplanètes est un domaine très actif. Malgré la nature indirecte de la plupart des détections, celles-ci nous fournissent déjà une quantité importante d'informations sur les propriétés de ces systèmes exoplanétaires: leur masse, taille et paramètres orbitaux. Pourtant, la détection directe de la lumière qu'elles émettent ou réfléchissent fournit des informations encore plus précieuses. Les instruments coronographiques conçus dans ce but sont généralement limités par la qualité de front d'onde, qui les empêchent notamment d'atteindre leurs performances théoriques. A l'inverse les techniques employant des observables qui sont robustes à ces aberrations sont limitées par le bruit de photon. Ces deux approches sont rendues incompatibles par la rupture de la relation de convolution qui lie l'objet à l'image. Les travaux décrits dans cette thèse explorent différentes avenues visant à contourner cette incompatibilité afin de combiner les performances des méthodes coronographiques et interférométriques, grâce à des transferts technologiques et au développement de nouvelles méthodes: Le développement des kernels différentiels angulaires (ADK) qui utilisent les principes de l'imagerie différentielle angulaire (ADI) dans le cadre des noyaux de phases et clôtures de phases. L'expérimentation de noyaux de phases avec une pupille apodisée. L'exploitation des noyaux de phases à partir d'images saturées. Le développement d'architectures exploitant les noyaux d'obscurité (kernel nulling) pour un nombre arbitraire de pupille, et notamment pour des architectures à grandes lignes de base. Ces travaux poussent les performances en contraste des observables robustes à faible séparation, et entament l'exploration des nouvelles voies du haut contraste robuste
The study of exoplanets has been a very active topic in the past years. Despite the indirect nature of most detections to date, those already provide us with a wealth of information on the properties of these exoplanetary systems, like their mass, size, and orbital elements. However, the direct detection of the light emitted or reflected by those planets provides some even more precious information. Coronagraphic instruments that would allow this are generally limited by the wavefront quality at their input, which prevents them from reaching their theoretical performance. Conversely, techniques employing observables designed to be robust to those aberrations are limited by photon noise. These two methods are made incompatible because coronagraphy breaks the convolution relationship betwen the object and its image. The works described in this thesis explore different avenues aiming to sidestep this incompatibility and to combine the performance of coronagraphic and interferometric methods though technology transfers as well as the development of new methods. The development of angular differential kernel phases (ADK) that make use the principles of angular differential imaging (ADI), transfering them for kernel and closure phases observables. The experimentation of kernel phases behind shaped pupil apodization masks. The exploitation kernel phases extracted from archival saturated images. The development of architectures for kernel nulling for an arbitrary number of apertures for Fizeau and long-baseline interferometry. These works push the contrast performance of robust observables at small angular separations and begin the exploration of new methods of robust high-contrast observations

Optical vortices are topological dislocations due to phase singularities in light beams carrying orbital angular momentum (OAM). The wavefront of the electromagnetic wave that carries OAM is twisted around its axis of propagation, with a helicoidal shape. Along the axis of the helicoid the phase is undefined, so the waves cancel each other out. Hence, the intensity distribution of a vortex presents a dark core due to the destructive interference, that is surrounded by a ’ring of light’. The vortex is characterized by a number, called the topological charge that indicates how many 2π-twists the wave does around the axis within one wavelength. In the past decade, the OAM of a beam was paid great attention in many applications in physics. Among these, the most promising are those in optical communications, nanotechnolo- gies, biology and astronomy. Optical vortices may be created by a variety of different methods, one of which is by the use of a diffractive vortex mask, the spiral phase plate. The spiral phase plate is a helicoidal device that looks like a spiral staircase with a certain number of steps, that imposes an azimuthally dependent phase retard on an incident optical wavefront. The object of the research presented in this dissertation is the study of the properties of these particular optical devices and some of their possible applications. Firstly, we have studied the spiral phase plate in the visible domain. We have found, through numerical simulations and experimental test on optical bench, a relationship between the number of steps, which build the phase gap, and the topological charge imposed to incident light beam. This result allowed us to optimize the design parameters of the spiral phase plates manufac- tured on PMMA for astronomical purpose. We have assembled our first prototype of the optical vortex coronagraph inserting in the optical path the spiral phase plate. Coronagraphs are instru- ments designed to block the light from a bright source so that nearby much fainter sources can be directly imaged without glare. The optical vortex coronagraph exploits the dark area in the intensity distribution of the even-topologically charged optical vortices produces by spiral phase plate, attenuating the light of the bright source keeping intact that of secondary sources. In this framework of our project we performed coronagraphic tests at Asiago 122 cm tele- scope extinguishing the light of one component of a stellar double system of almost one order of magnitude. The astronomical use of the spiral phase plate has suggested to us to investigate the efficiency of this device with respect to the angular distance at which the secondary source crosses the central singularity. Through numerical simulations we found that the optical vortex coronagraph works also above the limit posed by the Rayleigh criterion. The research has led to the proposition of a new method to determine the angular separation between two sources above sub-Rayleigh condition, exploiting the asymmetric intensity distribution of the OVs produced by a double system that crosses spiral phase plate. As Maxwell’s equations are equally valid for all the bandwidths, optical vortices can be pro- duced also in radio frequencies. Based on this fundamental principle, we have studied diffractive optics also for radio domain, presenting the first experimental evidence of a radio vortex. We built a reflective spiral phase plate made on styrofoam and aluminum, with a design based on the re- sults obtained in the visible domain. The experimental verification that OAM-carrying beams can be generated and exploited by using radio techniques has opened the way to the experiment that we carried out in radio communication. We have showed, in a real-world setting, that is possible to simultaneously transmit two radio channels on the same frequency encoded in two different orbital angular momentum states. This novel radio technique allows, in principle, the implementation of an infinite number of channels in a band centered on one and the same frequency. Our experimental findings that electromagnetic OAM can be used for radio and TV transmission are likely to open new perspectives on wireless communications and radio-based science.
I vortici ottici, sono caratteristiche topologiche dell’onda, legate alle singolaritá di fase nei campi elettromagnetici che trasportano momento angolare orbitale (OAM). Il fronte d’onda ha forma elicoidale, si attorciglia spiraleggiando attorno all’asse di propagazione in cui la fase é indefinita. Lungo l’asse dell’elica le onde fanno interferenza distruttiva le une con le altre, con il risultato di una distribuzione d’intensitá caratterizzato da una regione buia nel centro, circondata da luce a forma di ciambella. I vortici ottici sono caratterizzati da un valore, detto carica topologica che indica quante volte la fase compie una completa variazione di 360 gradi attorno all’asse ottico in una lunghezza d’onda. I vortici ottici possono essere prodotti con l’utilizzo di strumenti ottici. In particolare in questa tesi sono state studiate delle particolare ottiche diffrattive dette spirali di fase. Le spirali di fase sono ottiche il cui spessore cresce gradualmente intorno ad un asse; somigliano a scale a chioc- ciola, costruite con un certo numero di scalini ed impongono al fascio incidente un ritardo di fase che dipende dall’angolo azimutale. L’oggetto di questa ricerca é lo studio delle proprietá delle spirali di fase, la caratterizzazione e alcune possibili applicazioni. Lo studio si é inizialmente concentrato sulle spirali da fase nel range del visibile. Attraverso simulazioni numeriche ed esperimenti al banco ottico, siamo riusciti a ricavare una relazione tra il numero degli scalini che costruiscono il salto di fase nella spirale e la carica topologica che viene imposta al fascio incidente. Questo risultato ci ha permesso di ottimizzare i parametri di costruzione della spirale realiz- zata in PMMA per applicazioni astronomiche. Abbiamo infatti assemblato il primo prototipo di un coronografo a vortici ottici, nel cui cammino ottico é stata inserita la spirale di fase realizzata in base ai parametri da noi definiti. I coronografi, in generale, sono strumenti progettati per bloccare la luce proveniente da una sorgente brillante in modo tale da poter osservare direttamente delle sorgenti piú deboli nelle vicinanze. Il coronografo a vortici ottici sfrutta la regione buia nella di- stribuzione d’intensitá di un vortice ottico per attenuare la luce di una sorgente luminosa, senza diminuire l’intensitá della sorgente secondaria. Abbiamo testato il nostro prototipo al telescopio ’Galileo’ 122cm di Asiago, attenuando l’in- tensitá di una componente del sistema stellare doppio Epsilon2 Lyrae di quasi un ordine di magnitudine. L’applicazione astronomica della spirale di fase ci ha spinto allo studio delle sua efficienza, ovvero del contrasto che si ottiene nella zona buia del vortice ottico, a diverse distanze angolari della sorgente secondaria rispetto alla singolaritá centrale della spirale. Simulazioni numeriche hanno mostrato che il coronografo a vortici ottici funziona anche al di sotto del limite di risoluzione di Rayleigh. La ricerca si é sviluppata fino alla formulazione di un nuovo metodo per determinare la distanza angolare tra due sorgenti distanti meno del criterio di Rayleigh. Il nuovo metodo sfrutta la distribuzione d’intensitá asimmetrica dei vortici ottici prodotti dalla sorgente secondaria che passa attraverso la spirale di fase, ma non in corrispondenza della singolaritá centrale. Poiché le equazioni di Maxwell sono valide su tutto lo spettro elettromagnetico, i vortici posso- no essere prodotti anche in diverse bande rispetto al visibile. Basandoci su questo fondamentale principio abbiamo studiato delle ottiche diffrattive per la produzione di vortici nel range del radio. Abbiamo costruito con polistirolo e alluminio una spirale di fase basandoci sui risultati trovati nel visibile ed abbiamo ottenuto la prima evidenza sperimentale di un vortice radio. La verifica speri- mentale della possibilitá di generare e sfruttare vortici radio ha spianato la strada all’esperimento successivo che é stato condotto nel campo della comunicazione radio. Abbiamo compiuto la prima trasmissione OAM in cui due segnali sono stati trasmessi con- temporaneamente e sulla stessa frequenza, su due canali radio codificati in due diversi stati di momento angolare orbitale. Questa nuova tecnica radio permette, in teoria, di codificare un infinito numero di canali in una singola banda centrata su una frequenza. I risultati dei nostri esperimenti nel dominio del radio aprono nuove prospettive nel mondo della comunicazione.

This work explores remote sensing of planetary atmospheres and their circumstellar surroundings. The terrestrial ionosphere is a highly variable space plasma embedded in the thermosphere. Generated by solar radiation and predominantly composed of oxygen ions at high altitudes, the ionosphere is dynamically and chemically coupled to the neutral atmosphere. Variations in ionospheric plasma density impact radio astronomy and communications. Inverting observations of 83.4 nm photons resonantly scattered by singly ionized oxygen holds promise for remotely sensing the ionospheric plasma density. This hypothesis was tested by comparing 83.4 nm limb profiles recorded by the Remote Atmospheric and Ionospheric Detection System aboard the International Space Station to a forward model driven by coincident plasma densities measured independently via ground-based incoherent scatter radar. A comparison study of two separate radar overflights with different limb profile morphologies found agreement between the forward model and measured limb profiles. A new implementation of Chapman parameter retrieval via Markov chain Monte Carlo techniques quantifies the precision of the plasma densities inferred from 83.4 nm emission profiles. This first study demonstrates the utility of 83.4 nm emission for ionospheric remote sensing. Future visible and ultraviolet spectroscopy will characterize the composition of exoplanet atmospheres; therefore, the second study advances technologies for the direct imaging and spectroscopy of exoplanets. Such spectroscopy requires the development of new technologies to separate relatively dim exoplanet light from parent star light. High-contrast observations at short wavelengths require spaceborne telescopes to circumvent atmospheric aberrations. The Planet Imaging Concept Testbed Using a Rocket Experiment (PICTURE) team designed a suborbital sounding rocket payload to demonstrate visible light high-contrast imaging with a visible nulling coronagraph. Laboratory operations of the PICTURE coronagraph achieved the high-contrast imaging sensitivity necessary to test for the predicted warm circumstellar belt around Epsilon Eridani. Interferometric wavefront measurements of calibration target Beta Orionis recorded during the second test flight in November 2015 demonstrate the first active wavefront sensing with a piezoelectric mirror stage and activation of a micromachine deformable mirror in space. These two studies advance our ``close-to-home'' knowledge of atmospheres and move exoplanetary studies closer to detailed measurements of atmospheres outside our solar system.